Title: Tandem motors reduce well costs

Abstract

The new generation of tandem mud motors that recently appeared on the drilling scene is significantly affecting drilling efficiency worldwide. These motors provide drillers with increased horsepower at the bit, higher torque, and faster rates of penetration (ROP). With advanced engineering and more durable materials, motor life is being extended, thereby increasing the time between bit trips and reducing drilling costs. This article reviews the performance, design, and operation of these motors.

Running a positive displacement downhole motor with tandem power sections and the proper bit significantly increases the rate of penetration and reduces stalling problems. The use of positive displacement mud motors (PDMs) with two power sections has improved penetration rates on a number of drilling applications in western Canada. The majority of all the tandem motor runs to date have been successful. Results of these tandem runs show that tandem motors should be considered in any situation where a single motor is run. This paper reviews the performance of tandem motors at several case sites. It describes the design, ratemore » of penetration, bit selection, mud systems, and use in horizontal wells.« less

Improvements in integral joint connections (IJC) for casing in the past decade have allowed operators to drill wells previously not feasible to drill for economic or technology reasons. New integral joint connections can withstand greater loads, increasing their range of applications. The use of IJC casing can allow a slimmer well to be drilled, reducing total well costs. The paper describes integral joint connections, physical testing, computer technology, use in deep wells and deep water wells, drilling costs, and drawbacks.

Gas recovery on the Bongkot field has increased by 5% and well costs have decreased by 50% over a 4 year period. This was achieved by modifying the production strategy, and evolving well designs from classic multizone completions to tubingless monobore designs. Tubingless well designs have allowed a more aggressive perforating strategy, which taps gas reserves that were previously lost. Reduced consumable requirements and elimination of completion operations have contributed to lower overall well costs. This paper describes the process that led to the development of the tubingless design.

Tandem power section positive displacement mud-motors (TPS-PDMs) can increase penetration rate when used with tricone and PDC bits. This is achieved by increasing the available output torque and shaft rotational speed by reducing pressure drop per stage in the power section. Early PDMs were single-lobe 1:2 rotor-stator ratio motors. Horsepower produced by these PDMs was a result of high output-shaft rotational speeds and low output torque. Most later PDMs have rotor-stator ratios ranging from 3:4 to 10:11. This change to a higher ratio increased output torque, but also caused a decrease in rotational output-shaft speed. Motor power, a product ofmore » torque and speed, has not changed significantly in any particular motor size since the early PDMs. Modern day PDC and tricone ''motor'' bit use requires that PDMs provide high torque and medium to high (180- to 300-rpm) output shaft speeds. This paper discusses the four primary variables in the basic design of any PDM power section for a given diameter tool. Variables are: rotor-stator lobe ratio; lobe spiral pitch; maximum design pressure drop; and number of stages.« less

The following proposal is based heavily on exponential wear' functions. By simply slowing the main pump down to half rated speed and compensating with the other standby' pump at the same speed, each pump contributes an equal share of required output. This results in remarkable parts life increase, approaching well over twice that of conventional two pump standby' operations (one running and one standby) on typical rig systems. The corresponding reduction in mechanical maintenance is worth noting considering that, presently, the cost of pump parts may reach about $1 million over the life of two drilling rig mud pumps. Amore » single pump operated at reduced speed exhibits enormous parts life increase, but a second pump is needed to make up required output. Even though the number of parts is doubled there is still a relevant economic benefit from increasing parts life.« less